1. Technical Field of the Invention
The present invention relates to a technology for controlling an image of distance in the sense of hearing a sound when an audio signal is reproduced as the sound.
2. Description of the Related Art
A variety of technologies have been suggested to control a sense of the distance to a sound source given to a listener when a sound is reproduced, i.e., to control the distance to the sound source which the listener feels from the reproduced sound. For example, Patent Reference 1 suggests a technology in which an audio signal with a reflected sound component added to a direct sound component is generated through a reflected sound addition circuit, and the sense of distance given to the listener is controlled by adjusting the ratio of levels and the time interval between the direct and reflected sound components. Patent Reference 2 suggests a technology in which two sound reproducing units for direct and indirect sounds are provided and the sense of distance given to the listener is controlled by adjusting the ratio of levels between direct and indirect sounds reproduced by the two sound reproducing units.
[Patent Reference 1] Japanese Patent Application Publication No. Heisei 6(1994)-315200
[Patent Reference 2] Japanese Patent Application Publication No. Heisei 9(1997)-121400
[Patent Reference 3] Japanese Patent Application Publication No. 2004-80668
[Non-Patent Reference 1] The Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE, EA2004-3, SP2004-3 (2004-04), The Transfer Fuction Phase and the Distance from a Sound Source in a 3D Reverberation, Yoshinori TAKAHASHI, Mikio THOYAMA and Takashi MANABE.
The past technologies control the sense of distance given to the listener by adjusting an indirect or reflected sound added to the direct sound component. However, when a sound generated by a sound source is detected at a sound receiving point in a room, the distance between the sound source and the sound receiving point also exerts a great influence on phase characteristics of a minimum-phase component included in the direct sound component detected at the sound receiving point. In the past, there is no technology which takes this fact into consideration in controlling the sense of distance when a sound is reproduced.